CN108598389B - Lithium ion battery silicon-carbon negative electrode material and preparation method and application thereof - Google Patents
Lithium ion battery silicon-carbon negative electrode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a silicon-carbon cathode material of a lithium ion battery and a preparation method and application thereof. The method comprises the following steps: (1) carrying out high-temperature gasification treatment on the silicon powder to obtain gaseous silicon; then rapidly cooling to obtain nano silicon; (2) ball-milling the flake graphite, and drying to obtain nano graphite flakes; (3) adding the nano silicon into water, and adding a silane coupling agent to obtain a mixed solution A; then adding the nano graphite sheet and citric acid into the mixed solution A to obtain mixed solution B; (4) adding an organic carbon solution into the mixed solution B to obtain a mixed solution C, and performing spray drying to obtain a silicon-carbon composite material precursor; (5) and calcining the precursor of the silicon-carbon composite material in an inert gas environment to obtain the silicon-carbon negative electrode material of the lithium ion battery. The method has the advantages of simple process, convenient operation and suitability for industrial production, and the prepared silicon-carbon cathode material of the lithium ion battery has the advantages of excellent electrochemical performance, high specific capacity and good cycling stability.
Description
Technical Field
The invention belongs to the technical field of energy storage materials, and particularly relates to a silicon-carbon cathode material of a lithium ion battery, and a preparation method and application thereof.
Background
At present, the energy which is basically dominant in all countries is the traditional energy such as coal, oil, natural gas and the like, but with the rapid development of global economy, the excessive exploitation and use of non-renewable resources such as coal, oil, natural gas and the like lead to the increasingly reduced energy resource reserves, so the shortage of energy cannot meet the rapid development requirements of all countries in the world at present. Meanwhile, the use of a large amount of non-renewable energy sources such as coal, petroleum and the like also brings huge pollution problems to the environment: global warming, poor air quality, water pollution. Therefore, we have to develop sustainable energy, i.e. develop new energy that is renewable and low-pollution. Under the background of global energy shortage and environmental deterioration, energy storage batteries are advocated by the nation as power sources of electric bicycles, electric automobiles and other vehicles, and lithium ion batteries have the advantages of high energy density, long cycle life, no memory effect and the like, and are green energy storage and conversion devices. At present, lithium ion batteries have been widely used in the fields of portable electronic devices, power automobiles, and the like.
The graphite carbon negative electrode material has the advantages of good conductivity, abundant resources, no pollution and the like, and has successfully realized industrial application. However, the theoretical specific capacity of graphite is low (372mAh/g), the increasing demand of power energy can not be met, and the charge-discharge platform of the graphite is low (0.01-0.2V vs. Li/Li)+) The lithium precipitation on the surface of the graphite cathode is easily caused, and potential safety hazards exist. Currently, most studied lithium ion battery negative electrode materials are as follows: titanate, metal oxide, tin-based alloy, germanium-based, silicon-based negative electrode material and the like. The theoretical specific capacity of silicon is up to 4200mAh/g (Li)22Si5) The material is more than ten times higher than the commercialized graphite material (372mAh/g), so the silicon negative electrode material has huge application prospect. However, the pure silicon material as the negative electrode material of the lithium ion battery has the following problems: firstly, silicon belongs to a semiconductor and has poor conductivity; and secondly, the silicon can generate serious volume expansion in the process of lithium intercalation and deintercalation, so that the electrode material can be gradually pulverized in the process of multiple cycles to cause structural collapse, and further the problems of low first efficiency, short cycle life and the like are caused.
Aiming at the defects of the pure silicon electrode material, currently, many studied improvement schemes are as follows: nanocrystallization of silicon, porous silicon, alloying of silicon, and silicon-based compounding. The preparation method of the silicon-based negative electrode material comprises the following steps: the preparation method comprises the steps of reducing silicon dioxide by an aluminothermic method to prepare porous silicon, preparing nano-silicon by high-energy nano-ball milling, preparing silicon nanowires by CVD (chemical vapor deposition), preparing a silicon nano-film by magnetron sputtering, and preparing a silicon-based composite material (ball-milling mixing, spray drying, CVD carbon coating, liquid-phase organic carbon ex-situ coating, chemical in-situ polymerization coating and the like). The dispersion of the nano silicon in the silicon-carbon composite material and the stability of the carbon shell layer coated by the nano silicon are key factors of the high and low electrochemical performance of the silicon-carbon negative electrode material. Closed cycle spray drying has the advantages of: simple preparation process flow, solvent recycling, high drying speed and high yield, thereby being very suitable for industrial production. However, the silicon-based negative electrode material obtained by the existing method has the problems of larger irreversible capacity, poor conductivity, cycling stability and the like in practical application.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a preparation method of a silicon-carbon negative electrode material of a lithium ion battery.
The invention also aims to provide the lithium ion battery silicon-carbon negative electrode material prepared by the method. The silicon-carbon negative electrode material takes the flake graphite of the high-energy nano ball mill as a carrier, the first discharge specific capacity reaches more than 1300mAh/g, the first charge-discharge efficiency is high, the specific capacity is high, the cycle performance is stable, the rate capability is good, and the problems of larger irreversible capacity, poor conductivity, cycle stability and the like existing in the actual preparation and application of the existing silicon-based negative electrode material are solved.
The invention further aims to provide application of the silicon-carbon negative electrode material of the lithium ion battery.
The purpose of the invention is realized by the following technical scheme: a preparation method of a silicon-carbon negative electrode material of a lithium ion battery comprises the following steps:
(1) carrying out high-temperature gasification treatment on the silicon powder by using a radio frequency plasma system to obtain gaseous silicon; then rapidly cooling the gaseous silicon to obtain nano silicon;
(2) ball-milling the flake graphite, and then drying to obtain nano graphite flakes;
(3) adding the nano-silicon obtained in the step (1) into water, adding a silane coupling agent, and then performing ultrasonic dispersion to obtain a mixed solution A; adding the graphite nanoplatelets and citric acid obtained in the step (2) into the mixed solution A, and uniformly stirring and dispersing to obtain mixed solution B;
(4) adding the organic carbon solution into the mixed solution B obtained in the step (3), and uniformly stirring to obtain a mixed solution C; then carrying out spray drying on the mixed solution C to obtain a silicon-carbon composite material precursor;
(5) and (3) heating the silicon-carbon composite material precursor obtained in the step (4) in an inert gas environment to 400-600 ℃, keeping the temperature for 3-5 h at a constant temperature, then heating to 800-1000 ℃, and keeping the temperature for 3-5 h at a constant temperature to obtain the silicon-carbon cathode material of the lithium ion battery.
The high-temperature gasification treatment in the step (1) is preferably carried out by the following method: and putting the silicon powder into a radio frequency plasma system, and adjusting radio frequency current in the radio frequency plasma system to enable the inert gas to generate plasma beams, so that a high-temperature environment of 5000-12000 ℃ is realized, and the crude silicon is gasified into gaseous silicon.
The temperature of the high-temperature environment is preferably 9000-12000 ℃.
The radio frequency current is preferably 5.8-7.3A.
The inert gas is preferably argon.
The silicon powder in the step (1) is preferably 200-mesh (74 μm) silicon powder.
The rapid cooling in the step (1) is preferably rapid cooling using liquid nitrogen.
The speed of the rapid cooling in the step (1) is 100-500 ℃/min; preferably 250 to 500 ℃/min.
The particle size of the nano silicon in the step (1) is 20-100 nm; preferably 30 to 80 nm.
The flake graphite in the step (2) is commercial graphite which is purchased in the conventional market; flake graphite with the particle size of 11-20 mu m is preferred.
The ball milling in the step (2) is performed by adopting a high-energy nano wet method; preferably by the following steps: adding the crystalline flake graphite into water, stirring for 10-30 minutes, and adding into a high-energy nano ball mill for ball milling; wherein, the high-energy nanometer wet ball milling takes zirconia balls as grinding balls.
The water is preferably deionized water.
The average particle size of the zirconia balls is preferably 0.8-1.2 mm.
The ball milling conditions in the step (2) are as follows: ball milling at 3000rpm for 20-30 hr; preferably, the ball milling is carried out at 3000rpm for 25 hours.
The ball milling medium in the step (2) is preferably deionized water, ethanol or ethylene glycol.
The thickness of the graphite flakes in the graphite nanoplatelets in the step (2) is 80-200 nm;
the silane coupling agent in the step (3) is preferably KH-550.
The adding amount of the silane coupling agent in the step (3) is calculated according to the mass of the silane coupling agent accounting for 3-5% of the mass of the nano silicon; preferably calculated as 5% of the mass of the silane coupling agent in the nanosilicon.
The frequency of the ultrasound described in step (3) is preferably 20 kHz.
The time of the ultrasound in the step (3) is preferably 0.5-1 h.
The mixed solution B described in the step (3) is preferably obtained by: uniformly stirring the nano graphite flakes, the water and the citric acid obtained in the step (2), adding the nano graphite flakes, the water and the citric acid into the mixed solution A, and uniformly stirring and dispersing to obtain mixed solution B.
The stirring time in the step (3) is preferably 0.5-2 h.
The mass ratio of the nano silicon to the nano graphite sheet in the step (3) is 1: 2-4; preferably 1: 3.
The addition amount of the citric acid in the step (3) is calculated according to the mass of the citric acid accounting for 3-5% of the graphite nanoplatelets; preferably, citric acid is calculated as 3% of the mass of the graphite nanoplatelets.
And (4) stirring at the speed of 800-1000 r/min.
And (4) the solid content of the mixed solution C is 10-30%.
The mass ratio of the organic carbon in the organic carbon solution in the step (4) to the nano silicon is 4: 5.
The organic carbon solution in the step (4) is a pitch-tetrahydrofuran solution; preferably obtained by the following method: adding the asphalt into tetrahydrofuran, and uniformly stirring to obtain an organic carbon solution.
The amount of tetrahydrofuran is preferably 7.5mL of tetrahydrofuran per g (g) of pitch.
The stirring time is preferably 30 min.
The stirring time in the step (4) is preferably 1-3 h.
The drying in step (4) is preferably carried out by a closed cycle spray dryer.
The closed circulation spray dryer is a centrifugal atomizer, the rotating speed of the closed circulation spray dryer is 15000-40000 r/min, the inlet and outlet temperatures are 200-250 ℃ and 80-120 ℃ respectively, and the feeding speed is 10-20 mL/min.
The inert gas in the step (5) is nitrogen with the purity of 99.999% or argon with the purity of 99.999%.
The temperature rising speed in the step (5) is 1-5 ℃/min; preferably 2 deg.C/min.
A silicon-carbon negative electrode material of a lithium ion battery is prepared by any one of the methods.
The silicon-carbon cathode material of the lithium ion battery is applied to the field of preparation of electrode materials of lithium batteries.
The lithium ion battery negative plate comprises the lithium ion battery silicon-carbon negative electrode material.
The lithium ion battery negative plate also comprises a binder and a conductive agent.
The preparation method of the lithium ion battery negative plate comprises the following steps:
(I) and (3) mixing the lithium ion battery silicon-carbon negative electrode material, the binder and the conductive agent according to the ratio of (80-90): (5-10): (5-10) uniformly mixing the components in a mass ratio to obtain slurry;
and (II) coating the slurry prepared in the step (I) on copper foil, and carrying out vacuum drying and rolling to obtain the lithium ion battery negative plate.
The mass ratio of the lithium ion battery silicon-carbon negative electrode material, the binder and the conductive agent in the step (I) is preferably 8:1: 1.
The binder in step (I) is preferably binder LA132 or sodium carboxymethylcellulose (CMC).
The binder LA132 is a water-based binder produced by Chengdidenle corporation.
The conductive agent in the step (I) is commercial conductive liquid which is purchased in the conventional market; conductive carbon black Super-P or graphene conductive liquid is preferred.
The thickness of the coating in the step (II) is 90-160 microns; preferably 100 microns.
The vacuum drying conditions in the step (II) are as follows: drying for 10-24 h at 60-120 ℃; preferably: drying at 80 ℃ for 12 h.
The thickness of the rolled sheet in the step (II) is 70-140 micrometers; preferably 85 microns.
The principle of the invention is as follows: the conventional drying mode can not enable the nano-silicon to be uniformly dispersed on the surfaces of the two sides of the nano-graphite sheet, and in addition, the nano-silicon is easy to agglomerate, so that the problems of low initial efficiency, poor cycle performance and the like of the silicon-carbon cathode material of the lithium battery are caused. The invention adopts the radio frequency induction plasma technology to prepare the spherical nano-silicon, and the particle size of the particles is very small (20-100 nm); meanwhile, commercial flake graphite is mainly adopted, the flake graphite is ball-milled by a high-energy nano wet ball mill to obtain ultrathin nano graphite flakes (the particle size is 3-8 mu m and the thickness is 80-200 nm), then the silicon-carbon composite material powder is prepared by a closed cycle spray drying mode, two-dimensional nano graphite flakes are assembled into a three-dimensional mesh structure by spray drying and stacking, and nano silicon is uniformly dispersed on the surfaces of two sides of the nano graphite flakes and is coated by a carbon shell formed by organic carbon pyrolysis to form a core-shell structure.
In the invention, the nano silicon is dispersed by adopting the silane coupling agent, and the citric acid plays the role of an adhesive in the spray drying for preparing the silicon-carbon composite material, so that the nano silicon is uniformly dispersed on the surface of the nano graphite sheet. After carbonization, organic carbon such as citric acid and asphalt is carbonized into a porous carbon shell, so that the first efficiency and the cycling stability of the material are effectively improved. Therefore, the novel lithium ion battery silicon-carbon negative electrode material taking the nano graphite sheet as the carrier has the advantages of high first charge-discharge efficiency, high specific capacity, stable circulation and the like. Through a series of electrochemical tests, the first specific capacity of the lithium ion battery silicon-carbon negative electrode material obtained by the preparation method disclosed by the invention reaches more than 1300mAh/g, and is far higher than the theoretical capacity of the current commercialized graphite, namely 372 mAh/g.
Compared with the prior art, the invention has the following advantages and effects:
(1) the preparation method fully utilizes the advantages of the spherical nano-silicon prepared by the radio frequency induction plasma technology, has small particle size (20-100 nm), adopts silane coupling agent for surface dispersion and asphalt carbon coating, and obtains porous carbon shell after carbonization; carrying out high-energy nano ball milling on the flake graphite by using a high-energy nano ball mill to prepare nano graphite flakes; two-dimensional graphite nanoplatelets are assembled into a three-dimensional mesh structure by spray drying, and the nano silicon is uniformly dispersed on the surfaces of the two sides of the graphite nanoplatelets. The prepared three-dimensional mesh structure and the carbon coating shell effectively make full use of the advantages of high first efficiency and stable circulation of the nano silicon-carbon cathode material.
(2) The invention successfully solves the problems of large irreversible capacity loss, poor conductivity and poor cycle stability of the silicon-based negative electrode material in the prior art when the silicon-based negative electrode material is actually used for preparing the negative electrode of the lithium battery.
(3) The lithium battery silicon-carbon cathode material taking the nano graphite sheet as the carrier has the advantages of simple application process, convenient operation, low cost, high production efficiency and suitability for industrial mass production.
(4) The lithium battery silicon-carbon cathode prepared by the invention has the advantages of high first charge-discharge efficiency, high specific capacity, stable cycle performance and the like, can meet the requirements of high-capacity and long-life electronic equipment, and has wider application range.
Drawings
FIG. 1 is a diagram of an RF plasma apparatus for producing nano-Si according to examples 1, 2 and 3.
Fig. 2 is a XRD chart of the lithium ion battery silicon carbon negative electrode material prepared in example 1.
FIG. 3 is a scanning electron micrograph of the nano-silicon prepared in example 2.
Fig. 4 is a scanning electron micrograph of the flake graphite before nano-ball milling in examples 1, 2 and 3.
Fig. 5 is a scanning electron micrograph of nanographitic graphite sheets obtained after nanogrinmilling according to examples 1, 2 and 3.
FIG. 6 is a scanning electron microscope image of the silicon-carbon negative electrode material of the lithium ion battery prepared in example 3; wherein, the picture A is a scanning electron microscope picture (magnified by 2.0K times); panel B is a partial magnified view (20.5K magnification).
FIG. 7 is a cross-sectional scanning electron microscope image of the silicon-carbon negative electrode material of the lithium ion battery prepared in example 3.
Fig. 8 is a charge-discharge cycle curve of the silicon-carbon negative electrode material of the lithium ion battery prepared in example 3.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
Example 1
(1) Putting 10g of commercial crude silicon powder (with the particle size of 200 meshes and the particle size of 74 mu m) into a radio frequency plasma system (figure 1, 15KWind solution plasma system, Tecna plasma system company, Canada), adjusting radio frequency current to 5.8A, synchronously starting to perform inductive coupling on argon to obtain a plasma beam, enabling the temperature of a cavity of the plasma beam to reach 9000 ℃ high temperature, gasifying the crude silicon to obtain gaseous silicon, then starting a steam valve of the gaseous silicon to guide the gaseous silicon into a liquid nitrogen cooling bin (rapidly solidified through a condensation zone), wherein the cooling speed is 250 ℃/min, and the cooled and condensed nano-silicon powder is obtained, and the particle size of the nano-silicon is about 50-80 nm;
(2) adding 40 g of commercial crystalline flake graphite (the particle size of the commercial crystalline flake graphite is 11-20 microns as shown in a scanning electron microscope picture of figure 4) into 600mL of deionized water, stirring for 10-30 minutes, adding into a high-energy nano ball mill (the grinding ball is zirconia ball with the average particle size of 0.8-1.2 mm, and the ball milling medium is deionized water), rotating at 3000r/min, ball milling for 25 hours, and drying to obtain nano graphite flake powder. The scanning electron microscope image of the graphite nanoplatelets powder is shown in FIG. 5, the particle size of the graphite nanoplatelets is 3-8 μm, and the thickness is 80-200 nm.
(3) Adding 5 g of the nano-silicon powder prepared in the step (1) into 50mL of deionized water, adding 0.25 g of silane coupling agent (KH-550), and then performing ultrasonic dispersion (the ultrasonic frequency is 20kHz) for 30min to obtain a mixed solution I; then adding 15 g of the graphite flake nano-powder prepared in the step (2) and 0.75 g of citric acid into 150mL of deionized water, and stirring at a high speed (the rotating speed is 800-1000 r/min) for 30min to obtain a mixed solution II; adding 4 g of pitch into 30mL of tetrahydrofuran, and stirring for 30min to obtain a mixed solution III.
(4) Mixing the three mixed solutions obtained in the step (3), adding deionized water to enable the solid content of the whole dispersion system to be 20%, and shearing and stirring at a high speed for 30min at a stirring speed of 800-1000 r/min to obtain a mixed solution; then carrying out closed cycle spray drying on the obtained mixed solution to prepare powder, thus obtaining a precursor; wherein, the closed cycle spray drying is carried out in a closed cycle spray dryer which is a centrifugal atomizer with the rotating speed of 20000r/min, the inlet and outlet temperatures of 220 ℃ and 105 ℃ respectively and the feeding speed of 12 mL/min.
(5) And (3) placing the precursor prepared in the step (4) into a reactor, introducing nitrogen with the purity of 99.999% into the reactor, heating to 500 ℃ at the speed of 2 ℃/min, then preserving heat for 3h, then heating to 900 ℃ and preserving heat for 3h to obtain the novel lithium ion battery silicon-carbon negative electrode material taking the nano graphite sheet as the carrier.
And (5) carrying out XRD (X-ray diffraction) spectrum detection on the lithium ion battery silicon-carbon cathode material prepared in the step (5), wherein the detection result is shown in figure 2. The diffraction peaks of the nano graphite sheet and the silicon-carbon composite material and the diffraction peaks of the nano silicon and the silicon-carbon composite material are respectively compared and are all in line, so that the diffraction peaks of the nano graphite sheet and the silicon-carbon composite material and the diffraction peaks of the nano silicon and the silicon-carbon composite material are both opposite, and the silicon-carbon composite material is shown to have no carbon compound or silicide, namely, in the whole preparation process, the phases of the nano graphite sheet and the nano silicon are not changed, and the preparation process belongs to physical compounding.
And (2) uniformly mixing 0.8g of the silicon-carbon composite negative electrode material of the lithium ion battery, 0.1g of binder CMC (sodium carboxymethylcellulose) and 0.1g of conductive carbon black Super-P, mixing into slurry, coating the slurry on copper foil with the coating thickness of 100 microns, drying for 12 hours at the temperature of 80 ℃ in vacuum, and rolling (with the thickness of 85 microns) to prepare the negative electrode sheet 1 of the lithium battery.
The electrochemical performance of the button cell assembled with the electrode material of example 1 was tested using a LAND electrochemical test system at ambient temperature. And carrying out constant-current charge-discharge cycle test at a current density of 100mA/g (0.075C), wherein the voltage interval is 0.01-1.5V. And (3) testing results: the first discharge and charge specific capacity is 1323/1078mAh/g, and the first efficiency reaches 81.2%.
Example 2
(1) Putting 10g of commercial coarse silicon powder (with the particle size of 200 meshes and the particle size of 74 mu m) into an ultrahigh-temperature inductive plasma system (figure 1, 15KW Induction plasma system), adjusting radio-frequency current to 6.2A, synchronously starting an inductive coupling plasma beam to ensure that the temperature of a cavity of the inductive coupling plasma beam reaches 11000 ℃, gasifying the coarse silicon to obtain gaseous silicon, then starting a steam valve of the gaseous silicon to guide the gaseous silicon into a liquid nitrogen cooling bin, (rapidly solidifying through a condensation zone), and cooling at the speed of 350 ℃/min to obtain cooled and condensed nano-silicon powder (figure 3, a scanning electron microscope picture), wherein the particle size of the nano-silicon is about 40-60 nm;
(2) adding 40 g of commercial crystalline flake graphite (the particle size of the commercial crystalline flake graphite is 11-20 microns as shown in a scanning electron microscope picture of figure 4) into 600mL of deionized water, stirring for 10-30 minutes, adding into a high-energy nano ball mill (a grinding ball is a zirconia ball with the average particle size of 0.8-1.2 mm, and the milling medium is deionized water), rotating at 3000rpm, performing ball milling for 25 hours, and drying to obtain nano graphite flake powder. The scanning electron microscope image of the graphite nanoplatelets powder is shown in FIG. 5, the particle size of the graphite nanoplatelets is 3-8 μm, and the thickness is 80-200 nm.
(3) Adding 5 g of the nano silicon powder prepared in the step (1) into deionized water, adding 0.25 g of silane coupling agent (KH-550), and then performing ultrasonic dispersion (the ultrasonic frequency is 20kHz) for 30min to obtain a mixed solution I; then adding 15 g of the graphite flake nano-powder prepared in the step (2) and 0.75 g of citric acid into deionized water, and stirring at a high speed (the rotating speed is 800-1000 r/min) for 30min to obtain a mixed solution II; adding 4 g of pitch into 30mL of tetrahydrofuran, and stirring for 30min to obtain a mixed solution III.
(4) Mixing the three mixed solutions obtained in the step (3), adding deionized water to enable the solid content of the whole dispersion system to be 20%, and shearing and stirring at a high speed for 30min at a stirring speed of 800-1000 r/min to obtain a mixed solution; then carrying out closed cycle spray drying on the obtained mixed solution to prepare powder, thus obtaining a precursor; wherein, the closed cycle spray drying is carried out in a closed cycle spray dryer which is a centrifugal atomizer with the rotating speed of 22500r/min, the inlet and outlet temperatures of 220 ℃ and 105 ℃ respectively and the feeding speed of 12 mL/min.
(5) And (3) placing the precursor prepared in the step (4) into a reactor, introducing nitrogen with the purity of 99.999% into the reactor, heating to 500 ℃ at the speed of 2 ℃/min, then preserving heat for 3h, then heating to 900 ℃ and preserving heat for 3h to obtain the novel lithium ion battery silicon-carbon negative electrode material taking the nano graphite sheet as the carrier.
And (2) uniformly mixing 0.8g of the silicon-carbon composite negative electrode material of the lithium ion battery, 0.1g of binder CMC (sodium carboxymethylcellulose) and 0.1g of conductive carbon black Super-P, mixing into slurry, coating the slurry on copper foil to form a coating with the thickness of 100 microns, drying for 12 hours at the temperature of 80 ℃ in vacuum, and rolling (to form the negative electrode sheet 2 of the lithium battery, wherein the thickness of the negative electrode sheet is 85 microns).
The electrochemical performance of the button cell assembled with the electrode material of example 1 was tested using a LAND electrochemical test system at ambient temperature. And carrying out constant-current charge-discharge cycle test at a current density of 100mA/g (0.075C), wherein the voltage interval is 0.01-1.5V. And (3) testing results: the initial discharge and charge specific capacity is 1343/1117mAh/g, the initial efficiency reaches 83.2%, and compared with commercial graphite materials, the material has higher specific capacity and also has good cycle performance.
Example 3
(1) Putting 10g of commercial coarse silicon powder (with the particle size of 200 meshes and the particle size of 74 mu m) into an ultrahigh-temperature inductive plasma system (figure 1, 15KW Induction plasma system), adjusting radio-frequency current to 7.3A, synchronously starting an inductive coupling plasma beam to ensure that the temperature of a cavity of the inductive coupling plasma beam reaches 12000 ℃, gasifying the coarse silicon to obtain gaseous silicon, then starting a steam valve of the gaseous silicon to guide the gaseous silicon into a liquid nitrogen cooling bin (rapidly solidified through a condensation zone), wherein the cooling speed is 500 ℃/min, and obtaining cooled and condensed nano-silicon powder, wherein the particle size of the nano-silicon is about 30-50 nm;
(2) adding 40 g of commercial crystalline flake graphite (the particle size of the commercial crystalline flake graphite is 11-20 microns as shown in a scanning electron microscope picture shown in figure 4) into 600mL of deionized water, stirring for 10-30 minutes, adding into a high-energy nano ball mill (a grinding ball is a zirconia ball with the average particle size of 0.8-1.2 mm, and the milling medium is deionized water), performing ball milling at the rotating speed of 3000r/min for 25 hours, and drying to obtain nano graphite flake powder. The scanning electron microscope image of the graphite nanoplatelets powder is shown in FIG. 5, the particle size of the graphite nanoplatelets is 3-8 μm, and the thickness is 80-200 nm.
(3) Adding 5 g of the nano silicon powder prepared in the step (1) into deionized water, adding 0.25 g of silane coupling agent (KH-550), and then performing ultrasonic dispersion (the ultrasonic frequency is 20kHz) for 30min to obtain a mixed solution I; then adding 15 g of the graphite flake nano-powder prepared in the step (2) and 0.75 g of citric acid into deionized water, and stirring at a high speed (the rotating speed is 800-1000 r/min) for 30min to obtain a mixed solution II; adding 4 g of pitch into 30mL of tetrahydrofuran, and stirring for 30min to obtain a mixed solution III.
(4) Mixing the three mixed solutions in the step (3), adding deionized water to enable the solid content of the whole dispersion system to be 20%, and shearing and stirring at a high speed for 30min to obtain a mixed solution; then carrying out closed cycle spray drying on the obtained mixed solution to prepare powder, thus obtaining a precursor; wherein, the closed cycle spray drying is carried out in a closed cycle spray dryer which is a centrifugal atomizer with the rotating speed of 25000r/min, the inlet and outlet temperatures of 220 ℃ and 105 ℃ respectively and the feeding speed of 12 mL/min.
(5) And (3) placing the precursor prepared in the step (4) into a reactor, introducing nitrogen with the purity of 99.999% into the reactor, heating to 500 ℃ at the speed of 2 ℃/min, then preserving heat for 3h, then heating to 900 ℃ and preserving heat for 3h to obtain the novel lithium ion battery silicon-carbon negative electrode material taking the nano graphite sheet as the carrier.
Fig. 6 is a scanning electron microscope image of the novel lithium ion battery silicon-carbon negative electrode material, and fig. 7 is a scanning electron microscope image of a cross section of the novel lithium ion battery silicon-carbon negative electrode material.
And (2) uniformly mixing 0.8g of the silicon-carbon composite negative electrode material of the lithium ion battery, 0.1g of binder CMC (sodium carboxymethylcellulose) and 0.1g of conductive carbon black Super-P, mixing into slurry, coating the slurry on copper foil to form a coating thickness of 100 microns, drying at 80 ℃ in vacuum for 12 hours, and rolling (to form a thickness of 85 microns) to prepare a lithium battery negative electrode sheet 3.
The electrochemical performance of the button cell assembled with the electrode material of example 1 was tested using a LAND electrochemical test system at ambient temperature. And carrying out constant-current charge-discharge cycle test at a current density of 100mA/g (0.075C), wherein the voltage interval is 0.01-1.5V. And (3) testing results: the initial discharge and charge specific capacity is 1352/1141mAh/g, the initial efficiency reaches 84.4%, and compared with commercial graphite materials, the material has higher specific capacity and also has good cycle performance. Fig. 8 is a cycle performance curve of the novel silicon-carbon anode material of the lithium ion battery prepared in example 1.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (9)
1. A preparation method of a silicon-carbon negative electrode material of a lithium ion battery is characterized by comprising the following steps:
(1) carrying out high-temperature gasification treatment on the silicon powder by using a radio frequency plasma system to obtain gaseous silicon; then rapidly cooling the gaseous silicon to obtain nano silicon;
(2) ball-milling the flake graphite, and then drying to obtain nano graphite flakes;
(3) adding the nano-silicon obtained in the step (1) into water, adding a silane coupling agent, and then performing ultrasonic dispersion to obtain a mixed solution A; adding the graphite nanoplatelets and citric acid obtained in the step (2) into the mixed solution A, and uniformly stirring and dispersing to obtain mixed solution B;
(4) adding the organic carbon solution into the mixed solution B obtained in the step (3), and uniformly stirring to obtain a mixed solution C; then carrying out spray drying on the mixed solution C to obtain a silicon-carbon composite material precursor;
(5) heating the silicon-carbon composite material precursor obtained in the step (4) in an inert gas environment to 400-600 ℃, keeping the temperature for 3-5 h, then heating to 800-1000 ℃, and keeping the temperature for 3-5 h to obtain a silicon-carbon cathode material of the lithium ion battery;
the speed of the rapid cooling in the step (1) is 100-500 ℃/min;
the particle size of the nano silicon in the step (1) is 20-100 nm;
the graphite flakes in the graphite nanoplatelets in the step (2) have the particle size of 3-8 mu m and the thickness of 80-200 nm.
2. The preparation method of the silicon-carbon anode material for the lithium ion battery according to claim 1, wherein the high-temperature gasification treatment in the step (1) is realized by the following method:
putting silicon powder into a radio frequency plasma system, adjusting radio frequency current in the radio frequency plasma system to enable inert gas to generate plasma beams, realizing a high-temperature environment of 5000-12000 ℃, and gasifying crude silicon into gaseous silicon; the radio frequency current is 5.8-7.3A.
3. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps: the organic carbon solution in the step (4) is a pitch-tetrahydrofuran solution; the dosage of the tetrahydrofuran is calculated according to the proportion of 7.5mL tetrahydrofuran in each gram of asphalt.
4. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps:
the adding amount of the silane coupling agent in the step (3) is calculated according to the mass of the silane coupling agent accounting for 3-5% of the mass of the nano silicon;
the mass ratio of the nano silicon to the nano graphite sheet in the step (3) is 1: 2-4;
the addition amount of the citric acid in the step (3) is calculated according to the mass of the citric acid accounting for 3-5% of the graphite nanoplatelets.
5. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps: and (4) the solid content of the mixed solution C is 10-30%.
6. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps:
the ball milling medium in the step (2) is deionized water, ethanol or ethylene glycol;
the silane coupling agent in the step (3) is KH-550.
7. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps:
the ball milling conditions in the step (2) are as follows: ball milling at 3000rpm for 20-30 hr;
the frequency of the ultrasound in the step (3) is 20 kHz;
and (4) stirring at the speed of 800-1000 r/min.
8. The silicon-carbon negative electrode material of the lithium ion battery is characterized in that: prepared by the method of any one of claims 1 to 7.
9. The lithium ion battery silicon carbon negative electrode material of claim 8, and the application thereof in the field of preparation of lithium battery electrode materials.
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| CN111477861A (en) * | 2020-05-11 | 2020-07-31 | 四川聚创石墨烯科技有限公司 | Preparation process of silicon-carbon negative electrode material |
| CN113479890B (en) * | 2021-06-30 | 2022-12-27 | 松山湖材料实验室 | Silicon-based negative electrode material and preparation method and application thereof |
| CN113823780B (en) * | 2021-08-20 | 2023-04-11 | 广东邦普循环科技有限公司 | Silicon-carbon composite negative electrode material and preparation method and application thereof |
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